[Task]: drop CinderContentChange entity/class

[eviljeff]

Description

We're using the CinderContentChange entity to pass on what field values have changed. But moderators can rely on Cinder's attribute value change tracking instead

Acceptance Criteria

• CinderContentChange removed

┆Issue is synchronized with this Jira Task

[eviljeff]

Further thoughts on dropping ContentChange:

• there are still circumstances where we want to overtly differentiate a new submission; a changed add-on; and a re-review request. It’s unclear to me if there is any way to provide even a single string with an event to indicate the difference to a moderator, short of a separate entity (i.e. we might need to keep the ContentChange entity for the reasoning string).

• Localization. We currently send the Add-on entity metadata in the current locale each time it’s submitted with an abuse report. This is fine, because we can assume that’s what the abuse report was referring to. For content review though, we want all the localised strings to be reviewed by the moderator, and when values have changed they may have changed in the non-default locale. If we’re no longer sending the values added and removed in the ContentChange entity, we need to store and send all the localised values in the Addon entity instead (which isn’t necessarily a bad thing).

[eviljeff]

cc @abyrne-moz for the localization part - we don’t have a clear picture of how content review should work with translated values (in general, though this ticket is specific to the queue rendering).